This project has provided the first evidence that maternal responsiveness increases during pregnancy in pigtail and rhesus macaques and that treatment of ovariectomized rhesus females with estrogen increases significantly their interest in infants. Estrogen-treated ovariectomized females also increased their sexual interest in adult males without any concomitant changes in male behavior. This project has also investigated other aspects of female-and male-infant interactions in macaques including interindividual and interspecific variability in maternal cradling, infant nipple preferences, and mothering style. Finally, this project has continued an ongoing investigation of social communication dynamics within macaque groups, providing information useful to understand the social context in which adult females and males interact with infants. Altogether, these studies have enhanced our knowledge of the hormonal and social regulation of infant-directed behavior in macaques as we ll as our understanding of the relationship between social environment and communication systems in primates.